Antihalation backing for photographic films



June 15, 1937.- M. w. SEYMOUR 2,083,672

v ANTIHALATION BACKING FOR PHOTOGRAPHIC FILMS I Filed Jan. 8, 1935 DYE- SENSITIZED SENSITIVE LAYER ANTI'HALATION BACKING CONTAINING ACIDIC' AND BASIC FORMS OF WATER SOLUBLE INDOPHENOI. DYE IN EQUIMOLECULAR EQUILIBRIUM INVENTOR. mm. PM

Patented June 15, 1937 PATENT OFFICE ANTIHALATION BACKING roa rno'ro- FILM GRAPHIC Merrill W. Seymour, Irondequoit, N. Y., assignor, by mesne assignments, to Eastman Kodak Company, Jersey City,

New Jersey N. 1., a corporation of Application January 8, 1935, Serial No. 878

3 Claims.

"Ihis invention relates to photographic films, and more particularly to anti-halation backlngs for photographic films.

It is known to coat the rear face of photo- 5 graphic film with a layer containing a dye, in

order to prevent halation caused by the reflection of light from the back of the film. With photographic film whose emulsion layer is sensitized to certain colors of light, it is especially 1o desirable that light of the color or colors to which the emulsion is sensitized'should be prevented from reflecting back from the rear surface of the film.

I have discovered that the class of dyes known the water-soluble indophenol dyes are especially suitable for use in anti-halation backings on films whose emulsion layer has been sensitized by the incorporation of sensitizing dyes. Such films include, for instance, orthochromatic films, which are sensitized to yellowgreen light, and panchromatic films, which at sensitized to both yellow-green and red.

The water-soluble indophenol dyes are known to exist in two modifications absorbing light 26 strongly in different portions of the spectrum. The ratio of the two forms present in any given solution is determined by the hydrogen ion concentration. At a certain hydrogen ion concentration, which is specific for each dye, equi- 30 molecular concentrations of the two forms are a present in equilibrium, and consequently, the

absorption bands of both forms are present. A

solution of this composition absorbs light over a considerably greater region of the spectrum than 5 solutions containing almost entirely the one form or the other of the dye.

I have found that if a water-soluble indophenol dye is'incorporated into a gelatin solution containing such proportions of acidic and basic con- 40 stituents that, when the solution has been dried,

the two forms of the dye will be present in approximately equimolecular equilibrium, the gelatin solution containing the, dye may be advantageously used for forming an antihalation 5 backing on either orthochromatic or panchromatic film. In general, the concentration of dye used will be considerably higher than in solutions where it is used as an indicator of acid-base titrations, and the color of the layer will be correspondingly less sensitive to minute traces of acid or base which may be introduced from the atmosphere or the film support during the storage of the film. yIt should be kept in mind that there is usually av change in the equilibrium between the two forms of the dye upon drying down the backing. Thus, the dye which has the correct color at-the pH of the backing solution may not have the correct color when the backing has dried.

In the attached drawing,'l designates a support, such as cellulosic film or glass, 2 designates a dye-sensitized sensitive layer, such as an orthochromatic or panchromatic emulsion, and l designates an anti-halation or selectively light-' absorbing layer containing the acidic and basic forms of a water-soluble indophenol dye in approximately equimolecular. equilibrium.

The water-soluble indophenol dyes are red or pink in acid solution, and blue or greenish blue in alkaline solution. At. equimolecular equilibrium the mixture is purplish or-gray. The red form absorbs green light, and the blue form absorbs red light.-

The indophenol dyes, when used in the concentrations necessary for anti-halation purposes, are readily decoloriz ed by ordinary photo graphic developer solutions containing sodium sulfite. This is, of course, a necessary feature in a dye used for an anti-halation backing. An example of such a developer solution is the following:

El n 8.0 grams Sodium sulfite (desiccated) 400.0 do. Hydroquinone 20.0 do. Borax 8.0 do. Water to make 4.0 liters Presumably the sodium salt of the leuco-base of the dye is formed.

Although I may use the water-soluble indophenol dyes in equimolecular equilibrium, and

although, in equilibrium, they absorb .over a broad region of the spectrum, I have found that in this equilibrium they tend to have a lower total visual absorption thaneither of the two forms when present substantially alone. Also,

at equimolecular equilibrium some of the dyes phenol dyes which have their equlmolecular equilibria at sumciently low pI-Is exist predominantly in the blue alkaline form in the backing, have a greater optical absorption in the backing 5 than do equimolecular mixtures of the two forms, and, in fact, show sufficient absorption over the required ranges of the spectrum to be of value in anti-halation coatings for panchromatic film.

Although it is possible to adjust the composition of the backing solution so that any desired watersoluble' indophenol dye may be used, practical considerations make it more advantageous to select dyes which exist in the desired form in the i5 dried backing made from a solution of a predetermined composition. A plain solution of gelatin in water may be used as the backing solution, or sufiicient chrome alum may be added so that the gelatin hardens upon setting and drying, and 535 does not melt or become sticky under the conditions to which it is subjected. The pH of the solution is preferably adjusted to a value of about 5.5 to prevent premature setting of the gelatin, which would occur in a more alkaline solution. In my U. S. Patent No. 1,921,545 I have described and claimed the use of non-difiusin'g or water-insoluble indophenol dyes in screening layers which may be placed either upon the back of the film support or upon the surface of the emul- 39 sion layer. The water-soluble indophenol dyes are not particularly suitable for layers which are to be coated upon the emulsion layer, because of their di-fiusing character. However, they are entirely suitable for anti-halation backings or other screening layers coated on the back of the film support, because under proper storage conditions the anti-halation layer does not come in contact with the emulsion layer while either is in a moist condition. The use of the water-sol- 40 uble indophenol dyes has great advantages over the use of the insoluble indophenol dyes in layers where non-diffusibility of the dye is not essential, because of the vastly greater ease with which the soluble indophenol dyes are incorporated. The insoluble indophenol dyes must be formed in the gelatin solution, as by mixing two separately prepared gelatin solutions, or by drawing air through a gelatin solution for several hours. In any event, the resulting gelatin-dye emulsion must be cooled, shredded, washed and remelted, in order to free it from the soluble impurities formed or introduced. When the water-soluble indophenol dyes are used, all that is necessary is to add the required amount of the dye or of its sodium salt, to a warm gelatin solution, with stirring. The solution is then ready to coat immediately. No cooling, shredding, washing or remelting is necessary. It will be obvious that an enormous saving in cost is thus eifected.

As 'an example of a water-soluble indopenol dye whose two forms are in equimolecular equilibrium at a pH of approximately 5.5, I may mention 2 6-dibromobenzenoneindo-2 -'bromophenol, which has the structural formula 7 This dye has its equimolecular equilibrium at a pH of 6.3, but in a backing solution whose pH is 5.5, it gives a purplish mixture with broad absorption bands.

Examples of soluble indophenol dyes which give red backings which are useful on orthochromatic film are benzenoneindophenol, which has the structural formula G 3 0H and 2-methylbenzenoneindophenol, which has the 5 structural formula CH: o- N on Backing solutions oi pH 5.5 containing these dyes dry to give films that absorb principally between 460 my and 560 rn i. The dyes have their equimolecular equilibria at pl-Is of 8.1 and 8.4, respectively.

An example of a soluble idophenol dye which gives a blue backing which is useful on panchromatic film is 2 :6 dibromobenzenoneindo 3- methyl phenc-vl, which has the structural formula and has its e uiinolecular equilibrium at 5.4. Spectrophctometric examination of the dried 25 backing containing this dye shows that it has its absorption maximum in the red at about 630 um and its minimum in the blue at about 450 mp, but that its absorption band is sufiiciently broad, and

its absorption at the minimum sufficiently great, 30 to make the dye very useful as an anti-halaticn dye for panchromatic films.

Other soluble indophenol dyes, such, for instance, as 2:6:2'z6' -tetrabromoindophenol and 2:6 dichloroindonaphthol 3 sulfonic acid, are 35 likewise useful in anti-halation backings.

As examples of the way in which my invention may be carried out, I may prepare backing solutions as follows. 7

Example I.-Solution for a red hacking, especially suitable for orthochromatic film:

- Parts Sodium salt oi benzenoneindophenol l. Gelatin Water 10cc Example .iI.--So1ution for a blue backing, especially suitable for panchromatic film:

While above and in certain of the appended claims I have spoken of photographic film, it will 55 be understood that my invention is equally applicable to the preparation of anti-halation backings or other screening layers on the back of photographic plates.

. What I claim as my invention, and desire to be 60 secured by Letters Patent 01 the United States is:

l. A sensitive photographic element comprising a. support, a dye-sensitized sensitive layer, and a. selectively light-absorbing layer comprising, as its essential light-absorbing component, a water-sol- 55 uble indophenol dye, the sensitive layer and the selectively light-absorbing layer being on opp site sides of the support, and.' the acidic and basic forms of the indophenol dye being present in approximately equimolecular equilibrium.

2. A sensitive photographic element comprising a support, a dye-sensitized sensitive layer, and a selectively light-absorbing layer comprising, as its essential light-absorbing component, a watersoluble indophenol dye which is easily bleached by a photographic developing solution containing from the sensitive layer, an snti-halation hocking sodium sulflte, the sensitive layer and the seleclayer comprising, as its essential light-abnormal t velylie t-abso bi z layer b ing on Opposite sides component, a water-soluble indophenol dye. the

r 0f e p rt. and the acidic and basic forms of acidic and basic forms of the indophenol dye beta:

5 the d phenol dye bein present in ppm present in approximately equimolecular equllibl -mai:ely equimolecular equilibrium. rim. 4

3. A dye-sensitized, sensitive photographic ele- I HERB-11L W. SEYMOUR.

ment having, on the opposite side or the support 

